Swash plate type refrigerant compressor of a typical structure is disclosed, e.g., by Publication of Japanese Patent Application No. 3-92587 (1991), which includes front and rear cylinder blocks axially combined together to form a cylinder block assembly and having defined therein a plurality of pairs of aligned cylinder bores, a reciprocable double-headed piston fitted in each paired cylinder bores, front and rear housings bolted to the axial ends of the cylinder block assembly with a valve plate interposed between each housing and its adjacent cylinder block assembly end. The compressor further includes a drive shaft which is rotatably supported by bearings in the cylinder block assembly, and a swash plate fixedly mounted on the drive shaft at an angle of inclination for rotary wobbling movement in a swash plate compartment in the cylinder block assembly. The swash plate compartment communicates with a gas inlet fitting provided on the cylinder block assembly and connected to an external conduit through which refrigerant gas under a suction pressure is supplied to the compressor. Each double-headed piston is engaged with the swash plate by way of a pair of front and rear hemispherical shoes such that the wobbling movement of the swash plate is converted into reciprocating movement of the piston in its corresponding paired cylinder bores.
A pair of front and rear suction chambers are defined by the front and rear housings and their adjacent valve plates, respectively, and the swash plate compartment filled with refrigerant gas under suction pressure is connected with these front and rear suction chambers through a plurality of suction passages formed to extend axially through the respective cylinder blocks between any two circumferentially adjacent cylinder bores. Similarly, a pair of front and rear discharge chambers are formed on opposite ends of the compressor by the housings and the valve plates, respectively. These discharge chambers are connected to each other by way of passages extending axially through the cylinder block assembly so that compressed refrigerant gas discharged into one of the discharge chambers flows into the other discharge chamber, from where it is delivered out of the compressor together with refrigerant gas forced out directly into the above other discharge chamber.
Each valve plate has a flap or reed type suction valve for each cylinder bore, whose reed is flexible and operable to open a suction port in the valve plate during the suction stroke of the piston by a pressure differential then created between the suction chamber and the fluid working chamber associated with the piston. In the above-described swash plate type compressor, pressor, the refrigerant gas contains in it an appropriate amount of lubricating oil entrained thereby through the compressor in the form of a mist to lubricate various parts of the compressor such as bearings, sliding surfaces of parts. It is noted, however, that part of the oil sticks to the seat surface with which the suction valve reed is in contact when closed and that such oil offers resistance to the suction valve when its reed commences to be resiliently deformed or bent open by the pressure differential when the piston is moved for its suction stroke.
Because the flexible suction valve reed has to be resiliently bent to open the suction port, the pressure differential must be great enough to cause the reed to bend. That is, the reed itself, when it opens the suction port, offers resistance against the flow of refrigerant gas to be admitted into the cylinder bore. These resistances due to the lubricating oil and the reed itself cause a delay in opening of the suction valve thereby reducing the volume of refrigerant gas admitted into the fluid working chamber during the piston's suction stroke, with the result that volumetric efficiency of the compressor is reduced accordingly. Furthermore, the axial passages formed in the cylinder blocks extending between the swash plate compartment and the front and rear suction chambers cause a pressure loss of refrigerant gas passing therethrough, thereby affecting the working efficiency of the compressor.
It is noted that, for any given diameter of cylinder bores in a compressor, the bores should be arranged and spaced apart circumferentially from each other in the cylinder block assembly at such a spaced distance that maintains the desired wall thickness between any two circumferentially adjacent cylinder bores for ensuring the overall strength and durability of the cylinder block assembly. Arranging the cylinder bores radially toward the outer periphery of the cylinder block assembly with an attempt to increase the wall thickness will enlarge the assembly radially, thereby making the compressor disadvantageously larger in size. On the other hand, if the cylinder bores are arranged toward the axial center of the cylinder block assembly with an attempt to reduce the compressor size, the compressor strength will be in turn deteriorated by reduced wall thickness. As understood by those skilled in the art, the suction and discharge passages extending axially in the cylinder blocks are disadvantageous in that the presence of such passages reduces the wall thickness and, therefore, it is difficult to maintain the cylinder block assembly strength while achieving compactness of the compressor.